Which is why it always seems so odd to me that the Duchess of Sussex uses 'Meghan, Duchess of Sussex' now. It's the divorcee, ex-duchess way she would be referred to.
It's the same with the Cambridge children having Catherine, HRH The Duchess of Cambridge, on their birth certificates. It should be just HRH The Duchess of Cambridge, as Diana was HRH The Princess of Wales on William and Harry's and how Archie's corrected cert has HRH The Duchess of Sussex.
In the ridiculous bid to pretend that William and Harry's wives weren't going to be princesses they end up using butchered titles. Which is just stupid. If you're going to use a title at least use it properly!